As is well known, new and renewable energy is a solution to fossil energy depletion problems and environmental problems, despite there being an excessively large initial investment. In this respect, in advanced industrial nations, extensive research and development of new and renewable energy have been being performed and policies for the dissemination thereof have been adopted.
According to Article 2 of the Korean Act on the promotion of the development, use and dissemination of new and renewable energy, new and renewable energy is defined as energy that is obtained as a result of having converted fossil fuels or converting renewable energy, including sunlight, water, the heat of the earth, precipitation, biological oil, gas, etc. into energy. Also, the Act stipulates 11 new and renewable energy fields, that is, 8 renewable energy fields, including sunlight, solar heat, biomass, wind force, water power, ocean energy, waste and the heat of the earth, and 3 new energy fields, including fuel cells, coal liquefied gas and heavy residual oil gas, and hydrogen gas.
Integrated gasification combined cycle (IGCC) technology is a new technology in which low-grade raw materials such as coal or heavy residual oil are subjected to incomplete combustion and gasification with limited oxygen together with water vapor in a gasifier at high temperature and high pressure to make a synthesis gas containing carbon monoxide and hydrogen as its main components, which is then subjected to a refining process and used to derive gas turbines and steam turbines, thereby generating electricity.
For example, according to US Patent Publication No. 20060242907 (entitled “Gasifier Injector”), pulverized coal is injected into a gasifier through a plurality of branched tubes placed above the gasifier, wherein each of the injection tubes are passed through a plate made of porous material, and an oxidizer is fed through the porous material. Apertures are formed in the side of the branched tubes for supplying the pulverized coal, such that a major amount of the oxidizer is fed into the surroundings of the branched tubes, and the oxidizer fed through the apertures is rapidly mixed with the pulverized coal. A minor amount of the oxidizer passes through the porous material into the gasifier and flows downward from the entire upper region of the gasifier.
In the above patent publication, in order to rapidly mix the oxidizer with the pulverized coal which is fed into the gasifier through the plurality of branched tubes, the pulverized coal feed unit is passed through the porous material, the apertures are formed in the side of the feed unit so as to supply the oxidizer therethrough, and the oxidizer flows downward from the entire region except for the pulverized coal feed unit. However, because the pulverized coal and the oxidizer all flow downward vertically, a general slagging phenomenon in which pulverized coal particles melt and flow along the wall of the gasifier hardly occur. Thus, in the above patent publication, there is difficulty in realizing a slagging gasifier. Namely, a relatively large amount of the pulverized coal particles are discharged as particulate material. Also, it is impossible to control the flow rate of both the oxidizer flowing along the inner periphery of the pulverized coal feed unit and the oxidizer flowing around the feed unit, and thus it is difficult to cope with various operating conditions, including replacing fuel and changes in the flow rates of pulverized coal and oxidizer.
As another example, US Patent Publication No. 20080141913 (entitled “Dump Cooled Gasifier”) discloses a gasifier having a structure in which the wall of the gasifier comprises ceramic tubes and a gaseous or liquid coolant is allowed to flow into the ceramic tube so as to protect the inner wall of the gasifier from a high-temperature environment and high-temperature gas and slag during gasification. However, the gasification region is surrounded by the ceramic tubes made of ceramic material having weak mechanical strength, and for this reason, if the joint between the tubes is incomplete, the gasifier can be damaged in a high-temperature and high-pressure environment, thus making it difficult to stably operate the gasifier.
In most gasification technologies developed to gasify fuel such as coal or heavy residual oil into clean energy, a large-sized gasifier is used in order to complete a relatively slow gasification reaction in the gasifier. Despite this increase in the volume of the gasifier, when pulverized coal is used as fuel, it is difficult to completely convert carbon into gas.